1. Field of the Invention
The present invention relates to a wireless access system and, more particularly, to a method of a mobile station for efficiently requesting a bandwidth to a base station and a mobile station performing the same.
2. Discussion of the Related Art
Hereinafter, a protocol layer model being defined in a general broadband wireless access system will first be described.
FIG. 1 illustrates a protocol layer model defined in a generally used IEEE 802.16 system based wireless mobile telecommunications system.
Referring to FIG. 1, a MAC layer belonging to a link layer may consist of 3 sublayers. First of all, a Service-Specific CS (Service-Specific Convergence Sublayer) may modify or map data of an external network received through a CS SAP (Service Access Point) to MAC SDUs (Service Data Units) of a MAC CPS (Common Part Sublayer). A function of associating a respective MAC SFID (Service Flow IDentifier) and a CID (Connection IDentifier), after identifying the SDUs of the external network, may be included in this layer.
Subsequently, as a layer providing the essential functions of the MAC, such as system access, bandwidth allocation, connection set-up and management, the MAC CPS receives data from various CSs through the MAC SAP, wherein the received data are classified by a specific MAC connection. At this point, a QoS (Quality of Service) may be applied to data transmission and scheduling through a physical layer.
Furthermore, a Security Sublayer may provide Authentication, security key exchange, and encryption functions.
As a connection-oriented service, the MAC layer is realized by the concept of transport connection. When a mobile station (or terminal) is registered to the system, a Service Flow may be regulated in accordance with an agreement between the mobile station and the system. If a service request is changed, a new connection may be set-up. Herein, the transport (or transmission) connection defines a mapping between peer convergence processors using MAC and the service flow. And, the service flow defines QoS parameters of the MAC PDU, which are exchanged in the corresponding connection.
The service flow within the transport connection performs an essential role in operating a MAC protocol and provides a mechanism for QoS management of an uplink and a downlink.
In a general IEEE 802.16 system, the mobile station (or terminal) may have a universal MAC address having the length of 48 bits for each wireless interface. This address uniquely defines the wireless interface of the mobile station, and this address may be used for setting up the connection of the mobile station during an initial ranging procedure. Additionally, since the base station verifies each of the mobile stations with a different mobile station identifier (ID), the universal MAC address may be used as part of the authentication process.
Each connection may be identified by a CID (Connection IDentifier) having the length of 16 bits. While the initialization of the mobile station is under process, two pairs (uplink and downlink) of management connection may be set up between the mobile station and the base station, and, including a management connection, a total of 3 pairs may be optionally (or selectively) used.
Within the above-described layer structure, the transmitting end and the receiving end may exchange data or control messages through a MAC PDU (Medium Access Control Packet Data Unit). In order to generate such a MAC PDU, the base station or the mobile station may include a MAC header in the MAC PDU.
The mobile station may request for an uplink bandwidth by transmitting bandwidth request information in a MAC signaling header format or a MAC sub-header format. At this point, the mobile station requests for an uplink bandwidth in connection units between the mobile station and the base station. Hereinafter a general header structure will be described in detail.
FIG. 2 illustrates an exemplary MAC header format being used in an IEEE 802.16 system based wireless MAN mobile telecommunications system. Hereinafter, in the description of the present invention, in a block showing the header structure including FIG. 2, one graduation of indicates 1 bit, and one horizontal row indicates 1 byte. And, it is shown in FIG. 2 that, from top to bottom, the most significant bit (MSB) and the least significant bit (LSB) are sequentially arranged within the structure.
Referring to FIG. 2, in addition to a generic (or general) MAC header (GMH), 6 sub-headers may be used in the MAC PDU. A sub-header for each MAC PDU is inserted after the generic MAC header. Hereinafter, each field being included in the MAC header will be described in detail.
An HT (Header Type) field corresponds to a field indicating the header type. Herein, the HT field indicates whether the corresponding MAC PDU is a generic MAC header including a payload after the header or whether the corresponding MAC PDU is a signaling header for controlling a BR (Bandwidth Request). An EC (Encryption Control) field corresponds to a field indicating encryption control. Herein the EC header indicates whether or not the payload is encrypted. A Type field corresponds to a field indicating whether or not a sub-header comes after the header and also indicating the type of the sub-header. An ESF (Extended Subheader Field) field indicates whether or not an extension sub-header comes after the header.
Also, a CI (CRC Indication) field indicates whether or not a CRC comes after a payload. When a payload is encrypted, an EKS (Encryption Key Sequence) field indicates an encryption key sequence number being used for the encryption. A LEN (LENgth) field indicates the length of the MAC PDU. And, a CID (Connection Identifier) field indicates a connection identifier being delivered by the MAC PDU. Herein, the CID performs the function of identifying a specific mobile station or performs the function of identifying a specific service between the base station and the mobile station. And, an HCS (Header Check Sequence) is used for detecting an error of the header. In FIG. 2, the numbers shown in parentheses after the names of each field respectively indicate the number of bits occupied by each field.
FIG. 3 illustrates a MAC signaling header type 1 being used in a wireless MAN mobile telecommunications system, which is based on a generally used IEEE 802.16 system.
Referring to FIG. 3, since the Signaling header Type 1 corresponds to a signaling header, the value of the header type (HT) field is set to ‘1’, and the value of the encryption control (EC) field is set to ‘0’. The description of the type field is as shown in Table 1 below.
TABLE 1Type FieldMAC Header type (with HT/EC =(3 bits)0b10)000BR incremental001BR aggregate010PHY channel report011BR with UL Tx power report100BR and CINR report101BR with UL sleep control110SN report111CQICH allocation repuest
As shown in Table 1, depending upon the value to the type field, the Header Content field may have a different format. For example, when the type field has the value of “000” or “001”, the MAC signaling header is used as the BR (Bandwidth Request) header. The header format of this case will be described with reference to FIG. 4.
FIG. 4 illustrates an exemplary bandwidth request header being transmitted to a base station, when a mobile station requests for a bandwidth in the IEEE 802.16 system.
A detailed description on the fields included in the bandwidth request header shown in FIG. 4 is shown in Table 2 below.
TABLE 2LengthName(bit)DescriptionBR19Indicates the size of an uplink bandwidthrequested by the mobile station for thecorresponding CID in byte units. The requestis not influenced by a modulation or encodingof a physical layer.CID16Connection IdentifierEC1Set to 0 in the signaling header.HCS8Header check sequenceHT1Set to 1, being the signaling header.Type3Indicates the type of the Bandwidth Requestheader.
When requesting an uplink bandwidth by using the header as shown in FIG. 4, the mobile station may request for up to a maximum of 512 KB.
In a general system, e.g., in a system following the IEEE 802.16e standard, a bandwidth can be requested by using the above-described header. However, in the newly developed (or latest) system, e.g., in a wireless telecommunications system following the IEEE 802.16m standard (WirelssMAN-OFDMA advanced system only or WirelessMAN-OFDMA Reference System/WirelessMAN-OFDMA Advanced co-existing System), a more advanced and efficient method for requesting a bandwidth, as compared to the method used in the general system, is required to be defined.